EMD F7 in SCALE

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BigDumbDinosaur
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EMD F7 in SCALE

Post by BigDumbDinosaur » Mon Oct 19, 2015 11:58 pm

EMD F7 in SCALE
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This topic will chronicle some of my experiences in bringing a 1.6 inch scale EMD F7 Diesel-Electric locomotive from a whole lot of thoughts, sketches and drawings to the state of being a running model. This project has taken me far longer than expected—I've built considerably more complicated stuff in a fraction of the time, but I am making progress. The reasons for the slow progress are several, but this topic isn't the place to wax eloquent about them.

What set this project in motion was a visit to the Illinois Live Steamers (ILS) some 15 years ago and getting a good look at what large-scale railroading was all about. I've never had a lot of interest in table-top modeling and my years working in surface transportation on, around, under and in trains had given me the desire to own something that I could ride. After joining the ILS and finishing my probationary period, I started planning on acquiring a locomotive and some cars. I'm not real keen on buying ready-to-run stuff when I can build it myself, so that was the plan with the locomotive.

The choice of the F7 had to do with it being the very first locomotive I had ever set foot on and rode in—I was six years old at the time, and F7s were brand new in those days. As luck would have it, one of my relatives, who was an engineer for the Canadian National, was good buddies with someone who knew someone who arranged for me to tag along with a hostler as he shuffled units between the engine house and the yard. I got to ride in the cab and was taken on a tour of the engine room (that 16 cylinder Diesel looked positively gigantic to a six year boy). That experience cemented the F7 as "the one" in my young mind.

The F7, of course, has an illustrious history and was the motive power for a lot of fast varnish in the 1950s—all the more reason to build it. So my plan was to build a passenger engine. Choosing the road to model took some thought but I finally settled on the Chicago & Northwestern, specifically C&NW No. 401, and I would attempt to model its early 1950s appearance as closely as I could. I'm no rivet-counter but I also didn't want the thing looking like tinplate.
f7a_cnw_401_reduced.jpg
C&NW F7 Number 401
I should note that at one point during my first visit to the ILS, I did give some consideration to building steam. However, I ended up setting aside that idea. I was afraid that if I embarked on a steam project I'd probably be pushing daisies before I lit the first fire in the boiler. Ironically, that worry almost came to pass with the F7 project. :shock:

Anyhow, the goals for my F7 were simple:
  1. Reasonably accurate appearance. While I wasn't planning on counting rivets and bolts, I did want to have an exterior appearance that would give the illusion of the prototype as it might appear to a nearby mouse or gopher.
  2. Speed and tractive force commensurate with a scale passenger locomotive. In passenger gearing, the F7 was capable of a top speed of 102 MPH, and could develop about 52,000 pounds of starting tractive force, corresponding to approximately 13.6 MPH and 123 pounds tractive force in the model.
  3. Control response similar to the prototype. The real F-unit was electro-mechnically controlled, with the traction motor contactors pneumatically operated, and heavy use of magamps and saturable reactors. I was hoping to achieve something that would behave somewhat as though it was controlled in the same fashion.
There are also secondary goals, such as reasonably authentic lighting, air brakes, various noises and such, all of which would demand quite a bit of attention. Describing the processes that have gone into modeling the F7 in performance, as well as appearance, will take a few more posts. :)
f7a_no_sides.jpg
Erecting Bay at EMD c. 1950
Last edited by BigDumbDinosaur on Sun Oct 25, 2015 2:31 am, edited 1 time in total.
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BigDumbDinosaur
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EMD F7 in SCALE

Post by BigDumbDinosaur » Wed Oct 21, 2015 4:52 pm

EMD F7 in SCALE
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In order to model something you need to know something about that something. So my first step after deciding to model an F7 was to learn as much as I could about it. I wasn't exactly ignorant of what goes on inside a locomotive, but I did need specifics that would assist me in making good design choices. For example, I needed weights and dimensions in order to start making some sketches and translate a 50 foot long, 230,000 pound locomotive into a reasonably accurate scale equivalent. The Ixquick Internet search engine got quite the workout, saving me the indignities of having to paw through endless books and take endless notes during my information quest.

One of those searches netted me an image of an old EMD print for the F3, whose exterior dimensions are identical to the F7. I enlarged this image so I could reproduce it on two letter-size pieces of paper that could be taped together (I didn't have a large format printer available to me at the time). With that done, I could convert the full size dimensions to their scale equivalents—programmable pocket calculator to the rescue! :D
f7a_dimensions1.gif
F7A Dimensions Worksheet Cab End
f7a_dimensions2.gif
F7A Dimensions Worksheet Vestibule End
With basic dimensional information at hand I now knew roughly how big this beast was going to be—a bit more than 6-1/2 feet over the coupler pulling faces, and exactly 4 feet from one truck centerline to the other—and could turn my attention to just how I would build it. Here is where I made some very specific choices.

Most gas-engined model locomotives are more like riding lawnmowers than locomotives when viewed from a performance perspective. That wasn't at all what I wanted. I wanted a locomotive whose behavior would emulate that of the prototype in all respects. This meant that the engineer's controls and the propulsion system could not be the typical riding scale setup. Here are some of the features that I felt would be required to emulate the full sized F-unit:
  1. Power and speed solely controlled by a notched throttle with idle and eight power positions.
  2. Separate reverser mechanism with neutral, working independently of the throttle.
  3. Air brakes on both loco and control (riding) car.
  4. Automatic propulsion transition with manual override.
  5. Indefinite relationship between prime mover RPM and ground speed.
The above items would all be factored into the design, and would in turn, dictate how some things got executed. I'll go over all that in detail later on.

I had already made the preliminary decision to power it with a Briggs & Stratton V-twin engine, whose general design and performance characteristics are commensurate with what is required to power a large-scale model locomotive. However, before I could commit to the V-twin I needed more information about it, especially its physical size and wet weight. A couple of phone calls resulted in me acquiring some DXF CAD files of the V-twin.
briggs_v_twin.gif
Briggs & Stratton V-Twin DXF Drawing
The V-twin is mostly built to the metric system, which meant I found myself converting many dimensions to English sizes, resulting in more work for the programmable calculator.

Speaking of DXF prints, dimensions and such, and before I get too far along, I should mention something about drafting, as a lot of drawings (several hundred, in fact) were produced as this project proceeded. I use a relatively inexpensive two-dimensional CAD package called DeltaCAD to do my mechanical drafting. I have never liked AutoCad and as Microsoft's MS-DOS morphed (or degenerated, depending on your perspective) into Windows, AutoCad seemed to get clunkier, slower and more difficult to use. Everything I do in mechanical drafting is two-dimensional, so I don't need the capabilities (and expense) of three-dimensional CAD. DeltaCAD has worked out very well for me and I highly recommend it—versions exist for both the Mac and Windows. The below image was taken from a wheelset drawing I did in DeltaCAD, using the built-in export-to-image function.
wheelset.gif
Example DeltaCAD Drawing
Getting back to the F-unit's prime mover, the V-twin presents several engineering challenges, the most significant being that it is a 90 degree design and hence is pretty wide across the cylinder heads, making for tight quarters inside the unit (if only Briggs had used a 60 degree Vee—which I'm sure they didn't do because a two-throw crankshaft and a separate counterbalance shaft would have been required to produce a smooth-running engine). As the V-twin is air cooled, I had to ensure that adequate engine room ventilation was available, as well as carefully plan the machinery layout to keep things that don't like heat away from things that get hot.

The position of the oil filter on the V-twin is awkward, increasing the effective engine width to 16.75 inches—an oil filter sticking out of the side of the loco would be quite unsightly. The filter's obtrusiveness would have been a show-stopper if it weren't for the fact that its mounting bracket is removable and Briggs makes a remote filter mounting kit available. So one of the things I would have to do was find a new home for the oil filter, keeping in mind that it had to be readily accessible for routine servicing, and that it would be one of those hot things to be kept away from things that don't like heat.

Another consideration with the V-twin is its overall height of approximately 17-1/2 inches. In scale, the F7's height over the railhead is 22-1/2 inches, measured at the highest part of the roof. It was clear without even firing up a calculator that the V-twin's mounting in the loco would have to be relatively low to maintain interior clearance. Lowering the prime mover would mean that everything attached to it that had to be coincidental with the crankshaft centerline would be lowered as well, creating potential clearance issues with other parts of the loco's structure. As an aside, the dry weight of a 16 horsepower V-twin is approximately 90 pounds, and that weight is slightly asymmetric relative to the engine's crankshaft centerline.

Mentioning "structure" brings up yet another design point. The real F7 did not have a separate frame as is the case with modern locomotives, instead using a truss structure in the carbody to act as the primary load-bearing element of the unit. The body panels were riveted and bolted to this truss, adding some rigidity. Removable hatches in the roof that were attached with a gazillion bolts gave access to the engine room for removal and installation of the machinery (yep, the prime mover—all 30,000-plus pounds of it—had to be hoisted through the roof). Three such hatches were present: the main hatch, which also supported the radiator cooling fans; the dynamic brake hatch, which supported the dynamic brake grid cooling fan (if dynamic brakes were fitted); and the steam generator hatch located at the number two (vestibule) end of an A-unit.

From a modeling perspective, the F7's body design isn't very practical. If I had used it I would have been forced to install and remove the prime mover through the roof like the original, which given that the width across the cylinder heads approaches that of the body, would have resulted in an appearance grossly different than the prototype's. Servicing the machinery would have been very cumbersome. The only practical design is to use a rigid frame and relegate the body to a primarily cosmetic role. As it would be necessary to mount the prime mover and attached machinery relatively low in the unit, a drop-center frame would be necessary. I further decided to mount the body to the frame so that it would open like the body on a drag racing funny car, which would give access for refueling, routine maintenance and light repairs. The body would be completely removable for heavy repairs, just as is done with modern locomotives.

However, before I could design the frame, I needed to design the propulsion system, especially the "power assembly," which is what I call the amalgam of the prime mover and power transmission pieces that are attached to it. That will be described in my next post.
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Andrew Pugh
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Re: EMD F7 in SCALE

Post by Andrew Pugh » Wed Oct 21, 2015 11:30 pm

Very interesting project! I look forward to reading your future posts.

I believe I read somewhere that you are using a hydraulic drive; how do you plan to 'disconnect' locomotive speed from prime mover speed in such an arrangement?

-Andrew

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BigDumbDinosaur
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Re: EMD F7 in SCALE

Post by BigDumbDinosaur » Wed Oct 21, 2015 11:40 pm

Andrew Pugh wrote:Very interesting project! I look forward to reading your future posts.
I'll try not to take too long between updates.
I believe I read somewhere that you are using a hydraulic drive; how do you plan to 'disconnect' locomotive speed from prime mover speed in such an arrangement?
Well, I'll tell ya. There ain't nuthin' to it! :lol: How many times have you heard that over the years?

I'll go into the details in the next post. There really isn't much to it. :lol: All it is is some hydrodynamic magic mixed in with a little pneumatic control.
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Andrew Pugh
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Re: EMD F7 in SCALE

Post by Andrew Pugh » Wed Oct 21, 2015 11:45 pm

I'm looking forward to it. :D

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PRR5406
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Re: EMD F7 in SCALE

Post by PRR5406 » Thu Oct 22, 2015 10:37 am

I like the sharing of the design information. THis is going to allow somebody who might otherwise be put off, to get into his first project. Information is useless unless it's shared.
"Always stopping my train, and risking my ankles, with American made, New Balance sneakers."

redneckalbertan
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Re: EMD F7 in SCALE

Post by redneckalbertan » Thu Oct 22, 2015 9:01 pm

Enjoying your posts so far and looking forward to the upcoming ones.

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makinsmoke
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Re: EMD F7 in SCALE

Post by makinsmoke » Fri Oct 23, 2015 11:04 am

A couple of thoughts.

You might look at what others have done building EMD F units. May as well go to school on them and at the very
least not make mistakes they went through the trouble to
work through.

Frame-you might look at the standard blue box Athearn HO scale F unit. The shell is removeable from the frame, and although the frame is Zamac and very heavily engineered, may give you some ideas for yours.

Cooling. Why not install working fans in the roof? They would pull air through openings in the frame and push out the top, aided by warm air's tendency to rise. The wiring could be long enough or run in a way to allow the body to be raised, and a simple connector would allow complete removal as would the light wiring. Realistically,
just one working fan perhaps the dynamic brake fan would be sufficient to move enough air.

As far as exhaust I'd think I it would be cool to have the exhaust come out the correct openings in the top, but the noise, fumes and heat would be right in the engineers face.

A Railroad Supply unit with Kohler engine has two standard lawn mower mufflers teed off the main exhaust.
It actually has a better sound than my Rail Systems SW with Briggs 5.5 and proprietary exhaust.

There is somewhere on the Internet a very well designed muffler for these guys made from 2x4 tubing with several baffles. Maybe someone here has a lead on the thing.

I plan on trying one on my one lunger one of these days but it has real potential for a Vtwin.

Take care,
Brian

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makinsmoke
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Re: EMD F7 in SCALE

Post by makinsmoke » Fri Oct 23, 2015 11:14 am

One other thing regarding brakes on the engine.
Depending on the drive system it may not be
practical. For instance the "standard" hydraulic
drive with pump and motors on the axles as well
as hydrostatic transmission with mechanical
drive to the axles will stall and kill the engine if enough
brake is applied to the train. The last thing one wants
on a hill is losing your prime mover due to braking.

Just my two cents.
Brian

Andrew Pugh
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Re: EMD F7 in SCALE

Post by Andrew Pugh » Fri Oct 23, 2015 10:06 pm

Hello Brian,

I believe this is going to be a multi-part series on an already substantially complete locomotive, many years in the making.

I am certainly looking forward to learning about the drive and how it functions...

AP

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BigDumbDinosaur
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Re: EMD F7 in SCALE

Post by BigDumbDinosaur » Fri Oct 23, 2015 10:32 pm

Andrew is correct. This F-unit went from paper to reality some time ago. At this point in time, finishing and detailing the body is a major focus.
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Re: EMD F7 in SCALE

Post by ccvstmr » Sat Oct 24, 2015 7:46 am

"Science says it will work. Engineering makes it work."

...and then, good old-fashioned, ordinary common sense, kick in to fill the gaps where science and engineering couldn't explain why it didn't work! {sorry Bill, couldn't resist.}
Life is like a sewer...what you get out of it depends on what you put into it!
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